I would think it is more likely that the tree roots competing for moisture and food are depriving the rose of all the nourishment it needs. It might also be too shady for a rose bush planted under a tree.

Kate

Thank you so much Kate. It's been suggested that the tree be removed. It's a healthy beautiful tree.
The roses all receive full sun part of the day despite the tree. It's a mystery why the closest plants die and the farthest thrive.

Eastern red cedar (a juniper) is toxic (allelopathic) to some plants. The toxin is in the foliage. Note that western red cedar (not native to Colorado) is unrelated to the eastern kind.